I've been told off more than once in this series for employing military metaphors such as "redrawing the battle lines" and "truce". I accept the criticism: to talk in confrontational terms invites confrontation. However, I don't think that all such pleas for more moderation should be granted. In particular, there is a tendency to advocate suspended judgment rather than definite opinion as the appropriate response to thorny ultimate questions.

Given that the thermometer on the God debate has so often tended to indicate overheating, it is obvious why voices of calm and moderation seem attractive– and agnosticism is about as calm and moderate as you can get. It should, therefore, be clear why uncertainty appeals, but this very fact seems contrary to what you often hear.

For instance, Mark Vernon has borrowed from John Habgood (with full credit, of course) the phrase "the lust for certainty" to help explain what is wrong both with belief and unbelief. This is supposed to capture a malaise, perhaps contemporary, perhaps perennial, in which human beings crave fixed and certain truths in a fluid, uncertain world. It is a lust because it is excessive and irrational, and can never be sated. It therefore needs to be tamed, and agnosticism is the best way of doing so.

Vernon's advocacy of passionate agnosticism offers soothing camomile tea to those jittery after the triple espressos of the new atheists and religious fundamentalists. Since he is as genial in person as he is on the page, attacking him does feel rather like kicking a labrador puppy. But if we are serious about religion, being truthful must sometimes trump being nice, and intellectually, if not personally, Vernon needs a good kicking.

Vernon says: "We live in an age intolerant of doubt." But it seems to me that there is at least a class of educated, liberal westerners for whom the opposite is true. Uncertainty is what they desire more than anything else. This seems to me to have two sources, "dogmatophobia" and binary thinking.

What I call dogmatophobia is the liberal fear of being judgmental of the beliefs of others. Because everyone has a right to her opinion and no one has a monopoly on the truth, there is a tendency to think that any kind of assertion of a truth, other than of the blandest factual kind ("Paris is the capital of France"), is intolerant and morally imperialistic. Hence, people who assiduously avoid factory-farmed meat will go out of their way not to condemn ritual animal slaughter that causes needless suffering. People who would not tolerate even the sniff of sexism in their workplace bend over backwards to allow religious traditions their "right" to systemically discriminate against women.

This breed of excessively permissive liberalism – which is not the only kind, by the way – needs uncertainty to thrive. Where truths are even reasonably clear, there is no scope to say: "Who am I to say?" or "That may be true for you, but it may not be true to others." And so an understandable and generally laudable desire to be as inclusive and pluralistic as possible ends up with an unhealthy lust for uncertainty.

The second root of the problem is that people who officially embrace fuzziness of values are in other ways as hypnotised by clear but false dichotomies as anyone else. But there is no choice that has to be made between certainty and uncertainty. Rather, certainty is a matter of degree. It may be that nothing is certain, but not everything is equally uncertain. It is not certain that global warming is both real and anthropogenic, but that does not mean that those who advocate action on the belief that it is have fallen victim to a lust for certainty. The mistaken ones are those who make too much of this uncertainty and use it as a reason for inaction.

It is, of course, true that an excessive desire for certainty is deeply problematic. But pretty much every reasonable person agrees with this, and most are not agnostic. Accepting that the world is full of uncertainty and ambiguity does not and should not stop people from being pretty sure about a lot of things. To criticise people who express a firm belief as suffering from a lust for certainty is therefore to see the speck in another's eye while missing the plank in one's own: an excessive lust for uncertainty that makes any conviction appear misplaced.

The mark of a mature, psychologically healthy mind is indeed the ability to live with uncertainty and ambiguity, but only as much as there really is. Uncertainty is no virtue when the facts are clear, and ambiguity is mere obfuscation when more precise terms are applicable. Unfortunately, the middle ground in the God debate is occupied by too many people who screw up their eyes to create the illusion of a mist when the view is really clear. And this is not just wrong: it's dangerous, because if we make too much of our inability to be certain, we make ourselves incapable of clear and unequivocal condemnation of just those extreme dogmatists whom agnostics and moderate but committed believers fear. The main problem with young-Earth creationists who assert that the Earth is only 6,000 years old, for instance, is not that they are certain, but that they are wrong. It's the matter of the belief that is pernicious, not just the manner of its holding.

So of one thing we can be sure: it's high time we realised that adopting a moderate position in the God debate is not the same as adopting a non-judgmental one in which uncertainty becomes the new object of veneration.